( 15 ) 



an excess of liberated halogen the opposite reaction takes place, which 

 is quite in accordance with the regression of the latent image by 

 a bromide solution in the case of silver bromide, as found by 

 Lüppo-Cramer. 



The diffusion of liberated halogen will always take place in a 

 smaller degree in the series chlorine, bromine, iodine, on account of 

 the atomic weight rising. 



H. Luggin's rule must, therefore, be modified to the effect that in 

 the case of a certain definite light intensity the progressive and 

 regressive reduction get into a condition of equilibrium, which is 

 only got over by a loss of halogen (absorption by the chemical 

 sensitizer and diffusion). 



The same tiling was said in other words before now by J. Precht *), 

 but on the ground of the appearance of solarization. 



With this modified proposition of H. Luggin the deviations 2 ) from 

 R. Bunskn's and H. Roscoe's reciprocity rule 3 ) can be accounted for, 

 to which also belong the phenomena in the case of silver iodide 

 gelatine just mentioned. 



The knowledge of the latent image is arrived at by development. 

 While the exposure causes decomposition of the silver haloid accom- 

 panied by a quantitative increase in silver subhaloid, a decrease of 

 reducibleness appears during development after a certain maximum 

 of exposure. The solarization phenomenon is, therefore, a development 

 phenomenon in the sense that development, owing to the modified 

 properties of the latent image, shows a change. 



Consequently in order to account for solarization a knowledge of 

 the nature of development is requisite. Without it solarization remains 

 an unsolvable problem. 



Two methods of development are distinguished : The physical and 

 the chemical method 4 ). Physical development is characterized by a 

 deposit of a reduced silver compound from the developer on the 

 exposed silver haloid; chemical development by reduction of the 

 exposed silver halogen itself. 



*) Zeitschr. f. wiss. Phot. 1905. Bd. Ill; S. 75. 



2 ) J. M. Eder, Handb. d. Phot. 1906; Bd. I; T. 2; S. 48 u. 49. 



„ „ „ 1902; Bd. Ill; S. 228. 



„ „ „ 1898; Bd. II; S. 3 u. 5. 

 Phot. Mitt. 1890; 'S. 261. 

 Proc. Roy. Soc. 1893; Vol. 54; p. 143. 



3 ) Poggendorf Annal. d. Phys. 1862; Bd. 117; S. 538. 



4 ) J. M. Eder, Handb. d. Phot. 1898; Bd. II; S. 29. 



„ , „ 1906; Bd. I; T. 2; S. 250. 



